HD14 - The Virginia Quiet Pavement Implementation Program Under Section 33.1-223.2:21 of the Code of Virginia - Interim Report
Chapter 790 of the 2011 Virginia Acts of Assembly (Code of Virginia § 33.1-223.2:21; see Appendix A) provides, in part:
"The [Virginia Department of Transportation] shall expedite the development of quiet pavement technology such that applicable contract solicitations for paving shall include specifications for quiet pavement technology and other sound mitigation alternatives in any case in which sound mitigation is a consideration. To that end, the Department shall construct demonstration projects sufficient in number and scope to assess applicable technologies. The assessment shall include evaluation of the functionality and public safety of these technologies in Virginia's climate and shall be evaluated over two full winters. The Department shall provide an interim report to the Governor and the General Assembly by June 30, 2012, and a final report by June 30, 2013. The report shall include results of demonstration projects in Virginia, results of the use of quiet pavement in other states, a plan for routine implementation of quiet pavement, and any safety, cost, or performance issues that have been identified by the demonstration projects."
This interim report describes the selection of lower-noise pavement technologies (i.e., “quiet” pavement [QP]); the development and construction of the first season (2011) of QP demonstration projects; and the evaluation tools and analysis being used to compare the performance of the alternative strategies. When comparing noise levels of QP strategies, it takes about 3 decibels (dB) of difference for the change to be “noticeable” while a 5 dB change is considered “obvious”. After one winter of service, the quiet asphalt technologies were measurably (2 dB or less) less noisy than the control surfaces on average and noticeably (? 3 dB) more quiet in several specific cases. The featured quiet concrete technology, named the Next Generation Concrete Surface (NGCS), maintained an obvious (5 dB) noise advantage over the control concrete surface. The late fall tire-pavement noise testing showed that none of the surfaces had become louder over the very mild winter.
Traffic-generated noise comes from many sources. When travel speeds exceed 35 mph and the traffic stream is made up primarily of free-flowing passenger vehicles and light trucks, the predominant noise source is the tire-pavement interaction. The amount of noise generated at the tire-pavement interface is dependent on characteristics of the tire and the pavement surfaces. With regard to the traveled surface (i.e., pavement), the characteristics known to affect noise most include (in decreasing order of significance) texture, porosity, and stiffness. The contribution of each characteristic is complicated, but in most instances, a lower-noise (i.e., quiet) pavement will have a small, negative texture, a high porosity, and relatively low stiffness.
The category of materials known as open-graded or porous asphalt comes closest to having the optimum combination of properties that can deliver a quiet pavement. Use of these materials to reduce tire-pavement noise has been common in Europe since the early 1990s. Free-draining (i.e., porous) wearing surfaces offer other advantages as well, but early-generation open-graded mixes in Virginia were too often associated with premature and catastrophic material failures. Recent advancements have largely addressed the durability issues and enable designers to turn more specifically toward lower noise pavements.
The concrete pavement industry has also aggressively addressed the interaction of the tire and traditional concrete finishes. Recently developed diamond grinding and grooving techniques provide a highly uniform and lower-noise alternative for finishing existing concrete pavements.
Chapter 790 of the 2011 Virginia Acts of Assembly (Code of Virginia § 33.1-223.2:21; see Appendix A) directs VDOT to evaluate the installed QP technologies and provide an interim report in June 2012 and a final report in June 2013. The final report is to include
"results of demonstration projects in Virginia, results of the use of quiet pavement in other states, a plan for routine implementation of quiet pavement, and any safety, cost, or performance issues that have been identified by the demonstration projects."
Purpose and Scope
This interim report documents VDOT’s progress in implementing a quiet pavement use policy. It chronicles the selection of lower-noise pavement technologies, the development and construction of demonstration projects, and the evaluation tools and analysis being used to compare performance of the alternative strategies. The report will be particularly focused on results from testing conducted on the 2011 series of quiet pavement demonstration projects.
Preliminary Work of Task Force
As the 2011 legislation began to take shape in the fall of 2010, VDOT and the Virginia paving industry formed the Quiet Pavement Task Force (QPTF) in an effort to address the legislation cooperatively as it became enacted into the Code of Virginia. As listed in the Preface, the task force includes representatives from VDOT’s Materials, Maintenance, and Environmental Divisions; the Virginia Center for Transportation Innovation and Research (VCTIR); the Virginia Asphalt Association (VAA); the American Concrete Paving Association (ACPA); the Virginia asphalt contracting industry; and the Virginia General Assembly.
The QPTF was responsible for a number of critical early-project activities and decisions. Members worked with VCTIR to conduct a review of relevant literature (Appendix B). Further, the QPTF combined findings from the literature review with contemporary practical experience to develop a matrix of appropriate lower-noise materials and treatments. The QPTF established key requirements of the demonstration projects and engaged VDOT districts and contractors to identify suitable locations. Finally, the QPTF developed the material and construction specifications and helped assemble the contract documents that were used to advertise and award for construction.
Selection of Quiet Pavement Technologies
The QPTF selected three asphalt surface materials and two mechanically applied finishes to concrete pavement as candidate QP technologies for the 2011 demonstration projects. The three quiet asphalt materials included two open-graded asphalt concrete mixes that use a polymer-modified binder. The third uses a similar aggregate gradation but with a rubber-modified binder. The two lower-noise concrete technologies include conventional diamond grinding and the Next Generation Concrete Surface (NGCS), which is a diamond grind followed by a “flush-grind” operation and then a final longitudinal grooving step.
Selection of Demonstration Projects
VDOT used these five candidate QP technologies in five QP demonstration projects. These projects were made up of three new asphalt concrete projects and modifications to two existing concrete patching projects. The asphalt projects are located on the SR 7 Bypass in Leesburg, SR 199 west of Williamsburg, and SR 288 near Chester. The concrete sections are located on SR 76 in Richmond and I-64 near Virginia Beach. The asphalt demonstration projects each included four technologies: three experimental and one control. The concrete projects included the two QP technologies with the adjacent, existing (unground) concrete finish serving as the control.
The noise production and mitigating character of a candidate QP material or treatment is of obvious primary significance to this research. However, it is important to make sure that good noise performance does not come at the expense of safety and durability. Moreover, it is important also to document when reduced noise is accompanied by improved function in other respects. For this reason, the assessment of QP technologies considered tire-pavement noise, community wayside noise, ride quality, texture, resistance to skidding, and winter performance.
Porous wearing surfaces (i.e., the most common asphalt QP technologies) are widely known to respond differently than traditional materials to winter weather and winter maintenance tactics. The local maintenance crews received guidance on what to expect and how to report any exceptions to winter maintenance practices for QP surfaces during Virginia’s winter weather.
Preliminary Findings and Discussion
When comparing noise levels of QP strategies, it is important to understand that decibels are logarithmic units and cannot be added by normal arithmetic means. The Little Book of Quieter Pavements1, distributed in 2007 by the FHWA, describes the fundamentals of noise and its measurement, and includes some helpful rules of thumb. While precision instruments can measure small changes in sound level, the human ear requires about 3 decibels (dB) of difference for the change to be “noticeable”. A 5 dB change is considered “obvious” to most people and a 10 decibel difference is equivalent to a doubling (or halving) of the sound level.
As mentioned previously, as of spring 2012, the quiet asphalt technologies were measurably less noisy than the control surfaces on average and noticeably quieter in several specific cases (i.e., rubberized porous friction course near Williamsburg, coarser porous friction course in Leesburg). The NGCS maintained an obvious noise advantage over the control concrete surface. The late fall tire-pavement noise testing showed that none of the surfaces had become louder over the very mild winter. On the contrary, the sound intensity levels appeared to have dropped by varying amounts. A comparatively larger sound level intensity drop for the control surfaces makes it more difficult for the human ear to discern a difference between the QP technologies and the control surface on the asphalt projects.
The QP technologies have a more distinct advantage over the control surfaces with regard to ride quality. The NGCS is smooth, and contractors earned smoothness incentives with the quiet asphalt materials, including the materials that were placed at thinner (1-inch) application rates. Although some wheel path consolidation was evident from the texture data for the asphalt technologies, all of the QP surfaces have excellent skid resistance and are receiving consistent recognition for wet-weather service.